That was the question legislators tried to answer at Thursday's House Committee on Homeland Security hearing, where the members of Congress asked a former senator, Boston's top cop and two experts on public safety about whether or not the intelligence community dropped the ball when they closed an investigation into one of the alleged Boston bombers before the marathon bombing in April.

In opening the hearing, Republican Rep. Michael McCaul of Texas, the committee chairman, said he feared "the Boston bombers may have succeeded because our system failed. We can and we must do better."

"We learned over a decade ago the danger in failing to connect the dots," McCaul said, referring to the terrorist attacks of September 11, 2001.

One of the alleged culprits in the Boston bombing, Tamerlan Tsarnaev, 26, was investigated by the FBI after the agency received a tip from Russian authorities that the suspect could be radicalizing. Tamerlan, along with his 19-year-old brother, Dzhokhar Tsarnaev, allegedly carried out the April 15 marathon bombing, which killed three people and left 264 people wounded.

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Suspects tied to Boston bombings – Dias Kadyrbayev, left, with Boston Marathon bombing suspect Dzhokhar Tsamaev in a picture taken from the social media site VK.com. Kadyrbayev is expected to plead guilty August 21 to charges in connection with removing a backpack and computer from Tsamaev's dorm room after the April 2013 bombing, according to a defense lawyer.

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Suspects tied to Boston bombings – Bombing suspect Tamerlan Tsarnaev was killed during the shootout with police in Watertown, Massachusetts, on April 19, 2013. He is pictured here at the 2010 New England Golden Gloves.

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Suspects tied to Boston bombings – Dzhokhar Tsarnaev was captured in a Boston suburb on April 19, 2013, after a manhunt that shut down the city. In July, he pleaded not guilty to killing four people and wounding more than 200.

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Suspects tied to Boston bombings – From left, Azamat Tazhayakov and Dias Kadyrbayev went with Boston bombing suspect Dzhokhar Tsarnaev to Times Square in this photo taken from the social media site VK.com. A federal grand jury charged Tazhayakov and Kadyrbayev with obstructing justice and conspiracy to obstruct justice relating to the removal of a backpack from Tsarnaev's dorm room after the bombings. Tazhayakov was convicted of conspiracy and obstruction charges in July 2014. He faces up to 25 years in prison at his sentencing in October. He has filed an appeal.

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Suspects tied to Boston bombings – Robel Phillipos, a U.S. citizen, was also arrested on May 1, 2013. He was charged with lying to federal agents about the bombing, according to court papers.

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Suspects tied to Boston bombings – Phillipos, Tazhayakov and Kadyrbayev are accused of removing items from Tsarnaev's dorm room after the bombings on April 15, 2013. The items they took included a backpack containing fireworks that had been "opened and emptied of powder," according to the affidavit.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men identified as Suspect 1 and Suspect 2 in the deadly bombings at the Boston Marathon. They were later identified as Dzhokhar Tsarnaev, 19, and his brother Tamerlan Tsarnaev, 26.

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Suspects tied to Boston bombings – Boston Police released surveillance images of Dzhokhar Tsarnaev at a convenience store on April 19, 2013.

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Suspects tied to Boston bombings – The FBI tweeted this photo on April 19, 2013, and urged Watertown residents to stay indoors as they searched for the second suspect.

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Suspects tied to Boston bombings – The FBI released photos and video on April 18, 2013, of two men it called suspects in the deadly bombings and pleaded for public help in identifying them. The men were photographed walking together near the finish line.

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Suspects tied to Boston bombings – A man identified as Suspect 2 appeared in this photograph by bystander David Green, who took the photo after completing the Boston Marathon. Green submitted the photo to the FBI, he told Piers Morgan in an interview.

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Suspects tied to Boston bombings – The man identified as Suspect 2 appears in a tighter crop of David Green's photo.

Photos: Nation mourns Boston bomb victims – People pause at the memorial site in Copley Square on April 30 in Boston. The city continues to return to normalcy with Boylston Street fully reopened and businesses back up and running after two weeks of closures. See all photography related to the Boston bombings.

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Nation mourns Boston bomb victims – Running shoes are among the mementos left as a tribute to the victims of the bombing.

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Nation mourns Boston bomb victims – Boston shows its resilience and heart with signs of support for the marathon bombing victims, including this cover from the new issue of Boston magazine.

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Nation mourns Boston bomb victims – Law enforcement officials enter St. Patrick's Church in formation prior to the funeral for Massachusetts Institute of Technology Police Officer Sean Collier in Stoneham, Massachusetts, on Tuesday, April 23. Collier was allegedly shot and killed by Boston Marathon bombing suspects Dzhokhar and Tamerlan Tsarnaev on Friday, April 19.

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Photos: Nation mourns Boston bomb victims – Members of many different law enforcement agencies walk in formation into Collier's funeral at St. Patrick's Church on April 23.

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Nation mourns Boston bomb victims – President Barack Obama observes a moment of silence in honor of the victims of the Boston Marathon bombings, in the Oval Office in Washington on Monday, April 22. Massachusetts Gov. Deval Patrick asked his state and beyond to honor the victims at 2:50 p.m., the time of the first explosion.

Nation mourns Boston bomb victims – Nurse practitioner Maureen Quaranto, who treated victims of the Boston Marathon bombings, wears her Boston Marathon jacket during Mass at the Cathedral of the Holy Cross on Sunday, April 21, in Boston.

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Nation mourns Boston bomb victims – From left, Boston Police Department Superintendents Kevin Buckley and William Evans attend the Mass at the Cathedral of the Holy Cross with Police Commissioner Edward Davis on April 21.

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Nation mourns Boston bomb victims – Photos of the deceased are displayed at the Cathedral of the Holy Cross on April 21, the first Sunday since the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Boston Police Department Superintendent William Evans, right, kneels during the service at the Cathedral of the Holy Cross on April 21.

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Nation mourns Boston bomb victims – Parishioners gathered for a morning service at the Redeemer Fellowship Church on April 21, just a few blocks from the crime scene on Franklin Street where major police activity occurred on April 19 during the manhunt for Dzhokhar Tsarnaev, in Watertown, Massachusetts.

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Nation mourns Boston bomb victims – Leaders of an interfaith service participated in a vigil at the memorial for the victims of the Boston Marathon bombings, near the finish line on Boylston Street in Boston on April 21.

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Nation mourns Boston bomb victims – Crowds gathered to participate in an interfaith memorial service with leaders from six churches at a makeshift memorial for victims near the site of the Boston Marathon bombings at the intersection of Boylston and Berkeley streets on April 21.

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Nation mourns Boston bomb victims – The makeshift memorial honoring the victims of the Boston Marathon explosions on Boylston Street continues to grow as onlookers gather on April 21.

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Nation mourns Boston bomb victims – Nicole Collier Lynch, center, sister of slain MIT police officer Sean Collier, hugs a Wellesley police officer during a vigil at the Town Common in Wilmington, Massachusetts, on Saturday, April 20. Collier, 26, was shot multiple times in his car on Thursday night as Boston Marathon bombing suspects Dzhokhar Tsarnaev and his brother Tamerlan tried to evade capture.

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Nation mourns Boston bomb victims – A woman holds an American flag at a makeshift memorial on April 20, near the scene of the Boston Marathon explosions.

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Nation mourns Boston bomb victims – People gather at a makeshift memorial for victims on April 20.

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Nation mourns Boston bomb victimss – A flag decorates the memorial on Boylston Street in Boston on April 20.

Nation mourns Boston bomb victims – Items hang from a barrier Saturday at the makeshift memorial near the site of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Huntsville, Alabama, residents hold a prayer vigil on Friday, April 19, for those lost and injured in the bombing at the Boston Marathon. Three people died when two bombs went off Monday, April 15, near the finish line. View photos from the attacks.

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Nation mourns Boston bomb victims – A man rings a bell at the vigil in Huntsville on April 19.

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Nation mourns Boston bomb victims – Two women embrace during a candlelight vigil in Somerville, Massachusetts, for the victims of the Boston Marathon bombing on Thursday, April 18.

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Nation mourns Boston bomb victims – People hold candles as they listen to a speaker during a vigil in Somerville, Massachusetts, on April 18.

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Nation mourns Boston bomb victims – President Barack Obama talks with Massachusetts General Hospital staff on April 18 while visiting patients injured in the terror attack.

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Nation mourns Boston bomb victims – A man at the BoMA restaurant across the street from the Cathedral of the Holy Cross in Boston watches President Obama speak on television at the cathedral honoring the victims of the Boston Marathon bombings on April 18.

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Nation mourns Boston bomb victims – People watch President Obama at Cathedral High School in Boston on April 18.

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Nation mourns Boston bomb victims – A running shoe and U.S. flag are part of a memorial on the Boston Marathon route on April 18.

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Nation mourns Boston bomb victims – President Barack Obama and first lady Michelle Obama arrive at the interfaith service for the victims of the Boston Marathon bombing, at the Cathedral of the Holy Cross in Boston, on April 18.

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Nation mourns Boston bomb victims – Mourners filled the cathedral in Boston on April 18 for the the interfaith service.

Nation mourns Boston bomb victims – A flag flies at half staff on April 17 near the scene of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – First lady Michelle Obama takes part in a moment of silence for victims of the bombings at the Boston Marathon during a bill-signing ceremony at the Maryland State House in Annapolis, Maryland, on April 17.

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Nation mourns Boston bomb victims – Flowers, running shoes and other items are left in memory of Chinese graduate student Lingzi Lu, who was killed during the bomb explosions on April 17.

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Nation mourns Boston bomb victims – Joy Liu, 23, puts a green hat with a shamrock and a note with the words "From Boston and Beijing with love. RIP" at the memorial for Lu.

Nation mourns Boston bomb victims – Brooks Orpik of the Pittsburgh Penguins shows his support for Boston with a sticker on his helmet during the Penguins' game against the Montreal Canadiens on April 17.

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Nation mourns Boston bomb victims – A moment of silence was held for the victims of the Boston Marathon bombings before a hockey game between the Boston Bruins and the Buffalo Sabres on April 17.

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Nation mourns Boston bomb victims – People pray during a vigil held by the city of Cambridge, Massachusetts, on April 17 to show support for those affected by the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Dennis Seidenberg of the Boston Bruins observes a moment of silence for the victims of the Boston Marathon bombings before the start of an NHL hockey game in Boston against the Buffalo Sabres on Wednesday, April 17. It was the first sporting event held in the city since the bombings.

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Nation mourns Boston bomb victims – A man places a message for the victims of the Boston bombings at a memorial site in Boston on April 17.

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Nation mourns Boston bomb victims – Prior to an April 17 service at Marsh Chapel on the Boston University campus, members of the clergy walk past a memorial for graduate student Lu Lingzi, who was identified as the third person killed in the terror attack. Previously identified were Krystle Campbell, 29, of Arlington, Massachusetts, and Martin Richard, 8, of Dorchester, Massachusetts.

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Nation mourns Boston bomb victims – Danielle Cerroni writes a chalk message on the street on April 17 at the scene of the explosions near the finish line of the Boston Marathon.

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Nation mourns Boston bomb victims – Homeland Security Secretary Janet Napolitano observes a moment of silence for victims of the Boston bombing during a hearing before the Senate Homeland Security and Governmental Affairs Committee on April 17.

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Nation mourns Boston bomb victims – A woman looks at memorials left at the scene of the Boston Marathon explosions.

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Nation mourns Boston bomb victims – A man and woman leave after visiting the makeshift memorial on Boylston Street on April 17.

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Nation mourns Boston bomb victims – A mother and daughter hold one another during a vigil in memory of 8-year-old Martin Richard of Dorchester at Garvey Park in Boston on Tuesday, April 16.

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Nation mourns Boston bomb victims – A crowd holding candles gathers during a vigil on April 16 at Garvey Park in Boston for 8-year-old Martin Richard of Dorchester, who was killed in the marathon bombing.

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Nation mourns Boston bomb victims – People gather in Boston Common on April 16 for a candlelight vigil for victims of the bombings in Boston.

Nation mourns Boston bomb victims – Emerson College students embrace one another at the vigil on Boston Common on April 16.

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Nation mourns Boston bomb victims – Attendees hold candles in honor of the victims at an interfaith service at Arlington Street Church in Boston on April 16.

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Nation mourns Boston bomb victims – A woman uses her hand to keep wind from her candle as she stands with others around the pond in the Boston Public Gardens after a candlelight interfaith service at Arlington Street Church on April 16.

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Nation mourns Boston bomb victims – Mourners gather on the edge of the pond in the Boston Public Gardens for a candlelight vigil on April 16.

Nation mourns Boston bomb victims – Students from the Clifden Academy hold an American flag and candles during a vigil on April 16 in Dorcester, Massachusetts, in honor of 8-year-old Martin Richard, who was killed in the bombings.

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Photos: Nation mourns Boston bomb victims – People walk along the barricade at Boylston Street on April 16, following yesterday's bomb attack on the Boston Marathon.

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Photos: Nation mourns Boston bomb victims – On the shared porch of their home in Medford, Massachusetts, on April 16, Colleen Howe, left, and Lisa O'Leary grieve for their neighbor, Patty Campbell, who lost her daughter Krystle Campbell in the bombings.

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Photos: Nation mourns Boston bomb victims – Nicole Rand, left, who ran the marathon, embraces with her mother, Maureen Joham, on April 16 as she recounts her experience in Boston.

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Photos: Nation mourns Boston bomb victims – Attendees of the vigil sign a large poster in honor of the victims of the bombing on April 16.

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Photos: Nation mourns Boston bomb victims – Mourners hug one another during a vigil for victims of the Boston Marathon bombings at Boston Common

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Photos: Nation mourns Boston bomb victims – A man carries balloons, flowers and flags to a memorial for victims on April 16, just blocks from the scene of the bombings.

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Nation mourns Boston bomb victims – American flags hang from a barrier on April 16 at a roadblock staffed by National Guard soldiers at the end of Boylston Street near the site of the bombings in Boston.

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Nation mourns Boston bomb victims – Mike Vitale, who lives in the Boston area, prays beside a makeshift memorial at a roadblock at the end of Boylston Street.

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Nation mourns Boston bomb victims – Emerson College students Rachel Ferullo, left, and Kathryn Waxman at a vigil on Boston Common for victims of the bombings.

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Nation mourns Boston bomb victims – Runners Judy Adler, left, and her daughter, Rachel Schapiro, embrace during a moment of silence at the Baptist Health South Florida Brickell Run Club event organized on April 16 in Miami in honor of victims of the Boston Marathon bombings.

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Nation mourns Boston bomb victims – Five-time Boston Marathon runner Jose Sotolongo, center, reacts during a moment of silence at the Baptist Health South Florida Brickell Run Club event in Miami on April 16.

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Nation mourns Boston bomb victims – The New York Islanders and Florida Panthers stand for a moment of silence for the bombings at the Boston Marathon before their game at Nassau Veterans Memorial Coliseum on April 16 in Uniondale, New York.

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Nation mourns Boston bomb victims – Members of the Boston Red Sox observe a moment of silence before their game against the Cleveland Indians on April 16 in Cleveland.

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Nation mourns Boston bomb victims – People walk Boylston Street where memorials have been set up to the corner of Berkeley after the barricades were moved back on April 16.

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Nation mourns Boston bomb victims – A woman prays at a security gate near the scene of the bomb attack where visitors have congregated on April 16. See the aftermath in Boston.

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Nation mourns Boston bomb victims – From left, Boston Marathon runners Tammy Snyder, Diane Deigmann and Lisa Kresky-Griffin embrace at the barricaded entrance to Boylston Street near the finish line of the Boston Marathon on April 16.

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Nation mourns Boston bomb victims – Two young girls leave flowers on the steps outside the home of 8-year-old Martin Richards, who was killed in one of the explosions at the marathon.

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Nation mourns Boston bomb victims – Several former Heisman Trophy winners, including former Saints running back George Rogers, right, observe a moment of silence for the bombing victims Tuesday before working on a Habitat for Humanity home in New Orleans.

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Nation mourns Boston bomb victims – Traders observe a moment of silence on Tuesday before the opening bell on the floor of the New York Stock Exchange.

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Photos: Nation mourns Boston Marathon tragedy – The flag above the White House flies at half staff on Tuesday, April 16 in Washington.

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Nation mourns Boston Marathon tragedy – The Minnesota Twins stand during the national anthem before their game on Monday, April 15, in Minneapolis, following a moment of silence to honor the victims of the Boston Marathon bombings.

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Nation mourns Boston Marathon tragedy – President Barack Obama makes a statement about the bombings in the White House briefing room on Monday.

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Nation mourns Boston Marathon tragedy – Players and fans observe a moment of silence before the San Antonio Spurs and Golden State Warriors NBA game in Oakland, California, on Monday.

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Nation mourns Boston Marathon tragedy – A U.S. flag flies at half staff at the Capitol on Monday after House Speaker John Boehner ordered flags to be lowered.

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Nation mourns Boston Marathon tragedy – Fans pause for a moment of silence before the NHL game between the Phoenix Coyotes and the San Jose Sharks on Monday in Glendale, Arizona. See the world reaction to the attack.

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Photos: Nation mourns Boston bomb victims – Mark Trumbo of the Los Angeles Angels of Anaheim stands during the National Anthem following a moment of silence to honor the victims of the Boston Marathon bombing before the game against the Minnesota Twins on April 15, 2013 in Minneapolis, Minnesota. See all photography related to the Boston bombings.

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EXPAND GALLERY

Russian intelligence services asked the FBI to investigate Tamerlan Tsarnaev in 2011 over a possible association with terror groups. They later also asked the CIA. After receiving a tip, the FBI investigated Tsarnaev and, at the time, didn't find that he was engaging in any extremist activity.

The FBI said a three-month probe turned up nothing derogatory about Tsarnaev. The agency also said the Russians never responded to requests for more details. The case was closed.

Tamerlan Tsarnaev's name was put on a Customs and Border Protection list to alert officials in case he left the country and the CIA also asked that his name be added to another file, the Terrorist Identities Datamart Environment list, which contains more than 700,000 names of suspected foreign and domestic terrorists.

"Based on what I've seen so far, the FBI performed its duties, the Department of Homeland Security did what it was supposed to be doing," President Barack Obama has said.

Former Sen. Joe Lieberman, one of four witnesses at the hearing, told legislators that "though it would not have been easy, it was possible to prevent the terrorist attacks in Boston." Lieberman, who pushed for the creation of the Department of Homeland Security after the 9/11 attacks, said that post-9/11 reforms have worked well to protect Americans, but they are not perfect.

"I think that as a nation we need to come to terms with it and do everything we can to prevent it, but also recognize that fusion centers and intelligence analysis and joint terrorism task forces are part of our future," Davis said. "The world is a dangerous place and I think we need to recognize that and be prepared for it."

Republican lawmakers in particular were critical of the FBI for not following up on its initial investigation of Tsarnaev. In an exchange with McCaul, Davis acknowledged that if he had known about the initial FBI investigation, he would have done things differently.

"If you'd had this information before the bombing, would you have done -- your police force and you -- would you have done anything differently," McCaul asked.

"That's very hard to say," answered Davis. "We would certainly look at the information, we would certainly talk to the individual. "

McCaul continued to press Davis, asking "but if you knew of a Russian intelligence warning that this man's an extremist and made travel overseas and the fact that he did travel overseas and came back into the United States, would that may not have caused you to give this individual a second look?"

"Absolutely," said Davis.

In apparent response to the idea that the FBI did not inform Boston police of the investigation, the bureau issued a statement Thursday from Boston Special Agent in Charge Richard DesLauriers, saying the information was available.

The Boston Police Department has representatives on the Boston-area Joint Terrorism Task Force, he said, and all task force members can access Guardian, "a web-based counterterrorism incident management application that was launched in July 2004."

All task force members "are able to perform customized key word searches of Guardian to identify relevant" assessment of suspects, he said.

The assessment of Tamerlan Tsarnaev, one of about 1,000 conducted by the Boston task force in 2011, was "documented" in the Guardian database and "was thorough, comprehensive and fully compliant with law and policy," DesLauriers said. He noted that the task force is limited by law in "the types of investigative methods" it can use when there are no specific accusations.

In addition to revisiting the FBI's initial investigation into Tsarnaev, Davis used his testimony to say the Boston Marathon bombing is further proof the United States must strengthen vulnerable targets without violating civil liberties.

Before a hearing convened by the House Committee on Homeland Security, Davis submitted lengthy written testimony that touches on what worked and what didn't in the response to the Boston bombing. In that testimony, Davis argues that in order to defend soft targets -- locations that are not armored or are largely undefended -- law enforcement agencies need to "deploy more assets including technology, cameras, undercover officers and specialized units."

"It is clear after these events and other types of mass casualties such as those which have happened in our nation's schools and colleges that we need to continue to harden soft targets, especially events that lend themselves toward large gatherings celebratory in nature," Davis wrote.

However, Davis cautioned against overstepping the bounds of security. "I do not endorse actions that move Boston and our nation into a police state mentality, with surveillance cameras attached to every light pole in the city," he said.

After the bombing, Davis became the face of the response. Almost every legislator who asked questions in Thursday's hearing thanked him for his service.

Davis used that high-profile response as proof that reforms to the nation's video surveillance are needed, writing that in order to catch the bombers, law enforcement officials rely "almost exclusively on the support of our business partners to provide critical video surveillance along the finish line."

"I strongly support the enhanced ability to monitor public places," he wrote. "This monitoring, which been upheld by the United States Supreme Court, violates no constitutionally protected rights but gives police the ability to investigate and effectively prosecute. Images from cameras do not lie. They do not forget. They can be viewed by a jury as evidence of what occurred."

In the hunt for the Tsarnaev brothers, surveillance video proved crucial. Investigators solicited video from many of the business around the marathon route and used it to locate the bombing suspects. On April 18, the FBI released surveillance-camera pictures of the brothers.

Although Thursday's meeting is the first congressional hearing on the Boston bombing, it certainly will not be the last. Legislators in both the Senate and the House have expressed an interest in hosting experts to discuss what to learn from the terrorist attack.

The Boston bombing saga began after the two bombs went off at the Boston Marathon finish line on Boylston Street on April 15. Hundreds of Boston law enforcement officers then began a gripping week long search for those who carried out the terrorist attack.

Late at night on April 18, Massachusetts Institute of Technology police officer Sean Collier was shot and killed on campus, allegedly by the bombing suspects. In the early morning of April 19, the suspects allegedly hijacked a car in Cambridge and led police on a high speed chase through Cambridge and Watertown, two Boston suburbs. In a shootout during the chase, the older Tsarnaev brother was wounded by gunfire. He later died at a hospital.

Throughout much of that day, hundreds of law enforcement officers went door-to-door on 20 streets in Watertown, looking for Dzhokhar Tsarnaev. Residents around Boston were asked by authorities to stay inside as the hunt continues for the suspect.

In the early evening of April 19, David Henneberry discovered Tsarnaev, wounded, hiding in his boat. He alerted police, and after a tense standoff, police took him into custody.

Dzhokhar Tsarnaev, who was in serious condition at the time of his capture, is now stable and charged with one count of using and conspiring to use a weapon of mass destruction resulting in death and one count of malicious destruction of property by means of an explosive device resulting in death.

In addition to Tsarnaev, three 19-year-olds -- Azamat Tazhayakov, Dias Kadyrbayev, and Robel Phillipos -- were arrested in connection with the bombings. The three are accused of helping Tsarnaev after the bombing by taking items from his dorm room in an effort to keep them from investigators.